Preparation Of Supported Transition Metal Oxide For Catalytic Combustion Of Gaseous Dioxin

The process of refuse burning and steelmaking often produce amount of exhaust gas containing dioxin, which would impair the environment and people’s health. It is well known that dioxin is one of the most toxic compounds emitted from industry processes. It is urgent to dispose of dioxin with appropriate means. Among all the methods for dioxin treatment, catalytic combustion is the most feasible and economic for its low-energy and high degradation efficiency. In this paper, a series of supported transition metal composite oxide catalysts were prepared for catalytic oxidation o-dichlorobenzene (o-DCB) which acted as the model compound of dioxin. The effect of synthetic methods, ion doping, acid modification on their structures and catalytic performance were researched systematically.(1) A series of V-Ti catalysts were prepared via sol-gel method and used for catalytic oxidation of o-DCB. The results showed that the catalyst could have enough oligomeric active vanadium and its active components were well dispersed on the surface of TiO2when it was calcined at500℃with6%vanadia loading; The acid sites and the redox ability of V-Ti catalyst could be influenced by acid modification. The catalyst had more Br(?)nsted acid sites and showed better redox ability after SO42-and S2O82-modification, which enhance its catalytic activity. However, the PO42-modification led to the decrease of catalytic activity due to its poor redox ability.(2) A series of Fe-Mn-Ti composited oxide catalysts were synthesized by wet impregnation, sol-gel, co-precipitation and grinding method respectively. The catalyst was prepared by sol-gel with the Fe/Mn mole ratio1:1and calcined in500℃for4h giving the highest catalytic activity. It shows the total oxidation of o-DCB at about400℃and its activity can maintain in90%even after20h; The co-doping of Fe and Mn could suppress the phase transformation of TiO2from anatase to rutile in the products, and the change in calcination temperature could lead to the difference interaction between active species. The characterization studies of Fe-MnOx/TiO2showed that its active species (FeOx and MnOx) could be highly dispersed on the surface of TiO2, and the active species had a suitable interaction with TiO2. So the o-DCB molecules could contact with catalyst better during catalytic reaction, which was the reason why Fe-MnOx/TiO2showed the best performance in the catalytic oxidation of o-DCB.(3) FeOx-TiO2catalysts were prepared by solvothermal method. The mole ratio of Fe/Ti has great influence on catalyst’s structure. The active species (FeOx) demonstrate amorphous state on the surface of TiO2when Fe/Ti ratio is below or equal1, and Fe2O3crystal will emerge with the further increase of Fe/Ti ratio. The catalyst with Fe/Ti (mole ratio=1) showed the highest activity in the catalytic oxidation of o-DCB. Its degradation rate decreased rapidly with the increase of o-DCB concentration from80ppm to1350ppm, which indicate FeO^-TiO2is only suitable for the treatment of low-concentration dioxin. Besides, FeOx-TiO2showed better catalytic activity towards ethanol, dimethylbenzene than o-DCB.